A federal judge said sponsors of California's ban on same-sex marriage may not delay in handing over campaign strategy documents to gay-rights groups that are looking for evidence of anti gay bias as they try to overturn the measure.

The sponsors had sought to keep the documents while challenging the order to turn them over in an appeals court.

But in a ruling late Friday, Chief U.S. District Judge Vaughn Walker of San Francisco said backers of Proposition 8 had failed to show that disclosing internal memos and e-mails would violate their freedom of speech or subject them to harassment.

He said they had refused to identify any documents that needed special protection and noted that he could order their opponents to keep any sensitive material confidential.

"It simply does not appear likely that (Prop. 8's) proponents will prevail on the merits of their appeal," Walker said.

He said he doubts that a federal appeals court even has jurisdiction to consider the dispute at this early stage of the case.

Prop. 8, approved by the voters last November, amended the California Constitution to define marriage as a union of a man and a woman, overturning a May 2008 state Supreme Court ruling that granted gays and lesbians the right to marry their chosen partners.

The lawsuit by two same-sex couples, a gay rights organization and the city of San Francisco contends Prop. 8 violated the U.S. Constitution's guarantee of equality by discriminating on the basis of sexual orientation and gender. Walker has scheduled a trial in January.

Plaintiffs in the suit said documents from the Yes on 8 campaign might help them prove that the ballot measure was motivated by anti-gay bias, which would increase their chances of overturning it.

The measure's sponsors, a conservative religious coalition called Protect Marriage, said voters were entitled to reaffirm the traditional definition of marriage and that the organizers' alleged motives were irrelevant.

Walker ordered disclosure of the documents Oct. 1. In a court filing a week later seeking a stay, Charles Cooper, a lawyer for Protect Marriage, said the order would "cause future initiative proponents to censor their speech with campaign volunteers, donors, supporters and agents" and would "silence initiative supporters who wish to remain anonymous."